The present invention relates to an accumulator used for such purposes as accumulating and buffering a liquid under pressure and, more specifically, to a bladder-type accumulator with a movable cup-shaped sensor, which is adapted to detect a prescribed amount of liquid stored in a vessel body, by the use of a cup-shaped sensor provided in a bladder.
In a bladder-type accumulator, a set amount of gas is charged into a bladder provided inside a vessel body in an air-tight manner, and a fluid is introduced into or discharged from the space defined between the bladder and the vessel body in opposition to the pressure of the gas.
The amount of liquid stored in the vessel body is obtained by calculating it indirectly from change in pressure of the liquid, on condition that the pressure of the gas charged in the bladder is constant. However, it is impossible to obtain a correct amount of the stored liquid if the above-mentioned condition is changed by a factor such as gas leakage.
This is because, such a change in that condition causes a variation in the amount of liquid stored in the vessel.
To cope with this problem, it is the general practice to set the volume of the accumulator to a value larger than necessary.
If liquid of an amount greater than prescribed is introduced into the vessel body due, for instance, to gas leakage, the bladder is compressed beyond its allowable compression limit, and, as the amount of gas filling the bladder diminishes to none, the bladder is forced into a gas supply port or the like formed in the plug, and thus becomes broken.
If the bladder is broken in this way, the accumulator will suffer from gas leakage, hence, it will become unable to perform its functions such as the accumulation and buffering of a liquid under pressure. Therefore, such an incident can give a fatal damage to the accumulator.
To cope with the problem, it has hitherto been proposed to provide a holder projecting into the bladder inside the vessel body, and to fix first and second umbrella-shaped sensors to the holder with an interval therebetween, so that the amount of liquid stored is detected by the sensors (Japanese Utility Model Application No. 192944/1985).
With the bladder-type accumulator according to this proposal, detection is performed at two points within the bladder by the use of the two umbrella-shaped sensors. However, since these sensors are fixed, it is not possible to move the detection points or to perform detection with respect to a plurality of points by the use of one umbrella-shaped sensor. In order to perform detection with respect to a plurality of points, the number of umbrella-shaped sensors provided must be increased. From the viewpoint of design, however, it is almost impossible to provide more than two umbrella-shaped sensors on the holder.
As a result, it is difficult to effect detection at as many points as required, making it impossible to perform fine control. In addition, since an umbrella-shaped sensor has a lot of movable parts, it is vulnerable to the occurrence of failure.